Recently, as a digital still camera (hereinafter, referred to as a DSC) or the like have rapidly gained popularity, imaging lenses with high optical performance compatible with a large number of pixels equal to or more than five million pixels have been commercialized for use in an image input device recording a digital image. In addition, many mobile telephones or PDA terminals provided with a compact camera have been commercialized, and accepted in the marketplace. Among them, compact imaging units and imaging lenses compatible with a large number of pixels (two million to four million pixels) equivalent to that of a DSC are particularly gaining attention for use in, for example, compact cameras provided in mobile terminals or the like, in particular.
Conventional downsized imaging units and imaging lenses can be largely divided into two groups.
One is imaging lenses used mainly in mobile telephones for which downsizing and cost reduction are sought, PC (personal computer) cameras, PDAs, or the like, as disclosed in Japanese Laid-Open Patent Publication No. 2003-195158, for example. These are highly attractive in their sizes and costs and thereby commercialized in a large number, but not compatible with a large number of pixels, and, in many cases, they are only compatible with about one hundred thousand to three hundred fifty thousand pixels. A compact image sensor having an imaging quality of more than one million pixels is proposed, as disclosed in Japanese Laid-Open Patent Publication No. 2003-149547, for example. However, the number of lenses therein is as many as four or more, and a less expensive, compact type is sought for portability.
The other is in a field applied in endoscopes, surveillance cameras, or the like. The lenses achieve high optical performance and downsizing of some extent. However, the number of lenses therein is as many as six to nine to ensure the required performance, and portability and cost thereof do not allow a common use.